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--- magistraleinformaticanetworking:spd:2018:mandel [16/04/2018 alle 15:38 (7 anni fa)] – Massimo Coppola
+++ magistraleinformaticanetworking:spd:2018:mandel [18/04/2018 alle 15:03 (7 anni fa)] (versione attuale) – Massimo Coppola
@@ Linea 1: / Linea 1: @@
+==== Example code for mandelbrot ====
+C/C++ skeleton code for Mandelbrot computation.
 <code>
 #include <iostream>
@@ Linea 5: / Linea 9: @@
 #include "tbb/parallel_for.h"
 #include "tbb/blocked_range.h"
+// or use blocked_range2d if appropriate
 using namespace tbb;
 using namespace std;
-// costanti di default
+// default constants
-//square area, lower left angle and size
+// square area, lower left angle and size
 #define DEFAULT_X -2.0
 #define DEFAULT_Y -2.0
@@ Linea 18: / Linea 23: @@
 #define DEFAULT_ITERATIONS 1000
-// we assume a point diverges if quared modulus exceeds this value
+// we assume a point diverges if its squared modulus exceeds this value
 #define MAX_SMODULUS = 4
+// a variable holding the number of iterations limit
 static int maxIter = DEFAULT_ITERATIONS;
-//funzione per calcolo mandelbrot in un punto
+//function computing the mandelbrot in asingle point
 //returns the number of iteration until divergence
 int mand_compute( double cx, double cy)
 {
-    int i;
+ int i=0;
     double x = cx; double y = cy;
     double nx, ny;
@@ Linea 34: / Linea 40: @@
     {
        // (x,y)^2 + c
-       nx = x*x - y*y;
+       nx = x*x - y*y + cx;
-       ny = 2*x*y
+       ny = 2*x*y + cy;
        if ( nx*nx + ny*ny > MAX_SMODULUS ) break;
+       x=nx; y=ny;
     }
     return i;
 }
-// class to hold the computation
+// define class to hold the computation
@@ Linea 47: / Linea 54: @@
 int main () {
-// inizializza iterazioni
+// initialization
-// inizializza zona
+// inizialize data if needed
-//crea parallel range
+// parallel for
+// with blocked_range
-//parallel for
 }
 </code>
+==== Example code for saving an array as PPM graphics ====
+Compile and link this file together with you code.
+Remember to insert the function prototye in the main source file
+<code>
+#include <stdlib.h>
+#include <stdio.h>
+/** C routine to save a 2d int array as an image to a simple graphic format **/
+/** edited form of code from the rosetta code project **/
+/** https://rosettacode.org/wiki/Bitmap/Write_a_PPM_file **/
+int saveimg(int dimx, int dimy, const char * filename, int * matrix, int max_value)
+{
+  // filename must end with  .ppm
+  // no parameter checking!!! you are on your own
+  // const int dimx = 800, dimy = 800;
+  int i, j;
+  FILE *fp = fopen(filename, "wb"); /* b - binary mode */
+  (void) fprintf(fp, "P6\n%d %d\n255\n", dimx, dimy);
+  for (j = 0; j < dimy; ++j)
+  {
+    for (i = 0; i < dimx; ++i)
+    {
+      // here you may use any scaling function you prefer
+      int val = matrix[i +j*dimy];
+      if (max_value!=255)
+	{ val = (val *255) / max_value; // scale to 0 - 255
+	}
+      //
+      // rgb values are still rounded in case of mistakes
+      static unsigned char color[3];
+      color[0] = val % 256;  /* red */
+      color[1] = val % 256;  /* green */
+      color[2] = val % 256;  /* blue */
+      (void) fwrite(color, 1, 3, fp);
+    }
+  }
+  (void) fclose(fp);
+  return 0;
+}
+</code>